1. Field Of The Invention
The present invention relates to liquid crystal displays (LCDs) and, more particularly, to forming a high resolution active matrix LCD by a shadow mask deposition process.
2. Description Of Related Art
Active matrix backplanes are widely used in flat panel displays, such as LCDs, for routing signals to pixels of the display in order to produce viewable pictures. Presently, such active matrix backplanes are formed by use of a photolithography manufacturing process, which has been driven in the market by the demand for higher and higher resolution displays which are not otherwise possible with other manufacturing processes. Photolithography is a pattern definition technique that uses electromagnetic radiation, such as ultraviolet (UV) radiation, to expose a layer of resist that is deposited on the surface of a substrate. Exemplary photolithography processing steps to produce an active matrix backplane include coat photoresist, pre-bake, soak, bake, align/expose, develop, rinse, bake, deposit layer, lift off photoresist, scrub/rinse and dry. As can be seen, the active matrix backplane fabrication process includes numerous deposition and etching steps in order to define appropriate patterns of the backplane. Because of the number of steps required to form an active matrix backplane by use of the photolithography manufacturing process, foundries of adequate capacity for volume production of backplanes are very expensive.
A shadow mask deposition process is well known and has been used for years in microelectronics manufacturing. The shadow mask deposition process is a significantly less costly and less complex manufacturing process, compared to the photolithography process. However, the resolution achievable via the shadow mask deposition process is limited. Today's shadow mask manufacturing techniques are limited to forming, for example, up to 80 pixels per inch (ppi), which is representative of, for example, a typical laptop display resolution. However, for small displays, such as those in mobile phones and PDAs, a much higher resolution, on the order of 200 to 300 ppi, is desired. Because of this demand for higher resolution, active matrix backplane manufacturers have migrated away from the less costly and less complex shadow mask deposition process in favor of the photolithography process, but at the tradeoff of cost and complexity.
Furthermore, the shadow mask deposition process has other certain limitations that are well recognized in the industry. For example, the minimum aperture size and aperture spacing that can be produced accurately within a shadow mask is dependent on several factors, such as the thickness of the shadow mask and the overall area of the shadow mask, as is well known by those skilled in the art. The aperture size and aperture spacing also affects the overall strength and structural integrity of a shadow mask.
Therefore, what is needed is a way to provide a high resolution display, in particular a high resolution LCD, by use of the more cost-effective shadow mask deposition process, rather than by use of the complex and expensive photolithography process. What is also needed is a way to form a high resolution LCD by use of a shadow mask deposition process, while maintaining a minimum size and spacing of the apertures in the shadow mask(s) at a practical dimension.